Manufacturing of a laminated rotor core (hereinafter also simply referred to as the laminated core) 80 illustrated in FIGS. 5(A) and 5(B) is performed mainly by three steps including 1) laminating a plurality of iron core pieces 81 punched out from a steel sheet, 2) inserting permanent magnets 83 into provided magnet insertion holes 82, and 3) fixing the permanent magnets 83 by injecting resin 84 into the magnet insertion holes 82. In FIGS. 5(A) and 5(B), a numeral 85 represents a shaft hole, and a numeral 86 represents a laminated core body which is formed by laminating the plurality of the iron core pieces 81.
Normally, in any laminated rotor core, there exists an imbalance of weight in a circumferential direction of the laminated rotor cores, and due to an influence of the weight imbalance, lowering of performance of a motor such as inconsistency of motor torque is incurred. Accordingly, with respect to a largely imbalanced phase, an end face plate to be provided to an end in a shaft direction of each laminated rotor core is spot-faced to correct the weight imbalance.
However, an amount of correction achieved by spot-facing is limited, and this method cannot be applied to laminated rotor cores for which end face plates are not used. In each of the above-described main steps 1) to 3), there are factors causing the imbalance described below.
With regard to the step 1): Due to an influence from the time of rolling, a deviation of sheet thickness exists in a steel sheet, and a deviation of sheet thickness (t2-t1) also develops in each of the punched out iron core pieces 81 illustrated in FIG. 6(A). Accordingly, since the iron core pieces 81 are laminated in a rotational manner at the time of manufacturing a laminated core in order to resolve a problem of deviation of lamination thickness in the laminated core (hereinafter also referred to as the deviation of lamination thickness) caused by the influence of the deviation of sheet thickness, a deviation of lamination thickness t3 illustrated in FIG. 6(B) is alleviated. However, it is impossible to get rid of the deviation of laminated thickness t3 completely, and a weight balance becomes disproportionate.
With regard to the step 2): Since weights of the permanent magnets are unequal, a weight balance becomes disproportionate due to the difference in weight of the permanent magnets to be inserted in each of the magnet insertion holes.
With respect to step 3): Since the magnet insertion holes are bigger than the permanent magnets, the permanent magnets having been inserted lean to one side or become tilted in the magnet insertion holes, and positions and postures of the permanent magnets are irregular. When resin is injected into the magnet insertion holes in this state, a flow of the resin becomes affected by the positions and the postures of the permanent magnets and becomes unsteady, the positions and the postures in which the permanent magnets become fixed also become irregular, and the weight balance becomes disproportionate.
Among the above three particulars, with regard to the disproportion of weight balance incurred in the steps 1) and 2), as described in, for example, Patent Literatures 1 and 2, there is a correction method by which a weight is measured in a circumferential direction of a laminated core body (an iron core, a rotor body), weights of a plurality of permanent magnets are measured, or permanent magnets are processed and controlled so as to make the weight of each of the permanent magnets different, and the permanent magnets are fixed in the laminated core body in such positions that an imbalanced weight in the laminated core body is canceled out.